1. This application discloses a light-weight yet high strength piston pin for internal combustion engines and a method or process for manufacturing the piston pin. The pin is tubular with a normal cylindrical exterior surface, but has a double hourglass shaped aperture axially extending therethrough. This results in relatively thin walls near the pin's end portions and its midpoint and relatively thick walls therebetween. The aforedescribed shape closely approximates the extent of the bending moment and shear force input exerted on the pin by the action of the piston and the connecting rod.
The aforedescribed piston pin is difficult to make using conventional tooling. This is principally due to the double hourglass contoured aperture extending axially therethrough. Resultantly, the expanded diameter midportion of the double hourglass configuration is located between reduced diameter portions and is difficult to access with tools. Applicant has devised a method or process of manufacture which is both economical and efficient. First, a cylindrical slug of high ductility steel is placed in a bore of a die housing and between spaced, movable dies. The dies have tapered end portions adjacent the opposite end faces of the steel slug which are configured so as to form desired bore configurations of one half of a piston pin, i.e., opposite thin-walled end portions and a thicker midportion. The dies are forced toward one another to produce a half pin with thin end portions and a thicker midportion which includes a wall or web extending radially thereacross. Next, a punch is used to strike out the web. Then, two half pins are axially aligned and weld joined together to produce the aforedescribed double hourglass type piston pin. As a final step, the exterior cylindrical surface may be ground or polished, if necessary.
2. There have been attempts to use and produce tapered piston pins in the past. Prior pins known to applicant have included thinner end portions and a thicker midportion, but not the applicant's double hourglass interior configuration as heretofore described. Examples of such tapered pins or the like are found in U.S. Pat. Nos. 3,034,201; 3,314,266 and 4,290,236. All of these prior devices lack the specific characteristics of applicant's piston pin.
In addition to the unique configuration of applicant's piston pin over the devices in the above identified patents, applicant herein discloses a unique method of manufacturing the piston pin. None of the above identified patents disclose a similar method of manufacture.